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Plate Tectonics Earth layers History of plate tectonics Plate movement and margins Passive margins, spreading margins, and the Ring of Fire Ocean floor topography and plate tectonics Ocean floor effects: horizontal and vertical zonations Life Circulation Layers of the Earth Crust 4-60km Lithosphere 100km Mantle 2885km Asthenosphere 250km Outer core 2270km Lower mantle 2550 Inner core 1216km Outer Core Inner core Earth topography Movement of Continents Old views: Geosyncline cycle no continent movement Instead, continent growth through sediment accretion Movement of Continents Alfred Wegener: Plate Tectonics: 1912 Continents like “puzzle pieces” Fossils on different continents Carey and the Southern Hemisphere geologists Movement of Continents Morey: Canada Hess: mantle convection and sea floor spreading Continental Drift: theory Movement of Continents Vine and Matthews: tested Continental Drift Magnetic “stripes” Magnetic reversals Symmetrial Theory of Plate tectonics accepted. Istostacy Density differences Density: closeness of molecules Mass/volume Istostacy: Crustal floatation on the mantle Like ice cube: part above the mantle surface part beneath “Root” balances “top”: floats in equilibrium Ocean crust more dense, floats lower Plate Movement: Cross Section Active Margin Divergent Plate Boundaries Crustal formation, spreading Mid-ocean ridges mantle convection upward volcanism new crust made Begin in continent Africa/South America African rift valley Volcanoes, earthquakes African Rift Valley Rifting Gondwana Active Margin Convergent Plate Boundaries Subduction: destructive Ocean - ocean Island arc Japan Ocean-continent Continent-continent Volcanoes, earthquakes, trenches Active Margin Convergent Plate Boundaries Subduction: destructive Ocean - ocean Continent - ocean Volcanic arc Andes, Cascades Continent - continent Volcanoes, earthquakes, trenches Active Margin Convergent Plate Boundaries Subduction: destructive Ocean - ocean Continent - ocean Continent - continent: tall mountains Tibetan plateau Volcanoes, earthquakes, trenches Active Margins: Transform Boundaries Neither constructive nor destructive Strike-slip, shear: 2 plates slide San Andreas Earthquakes no volcanoes Passive Margins Stable margins Development of wide continental shelf or ramp East coast North America Mountains from previous continent-continent collisions Small earthquakes from ancient faults But no effects from margin Hot Spots Mantle plumes: “stationary” as plates move over them Record of plate movement Land or ocean Land: Yellowstone Ocean: island formation Hawaii Hot Spots Superplumes in Cretaceous: High rates of sea floor spreading: Ocean crust warm --> sea level much higher Sundance Sea CO2 into atmosphere: greenhouse effect Ocean Depths Ocean Depths Supralittoral zone: “spray zone”: terrestrial Littoral zone: tidal range Sublittoral zone Inner sublittoral zone: 050m Outer sublittoral zone:50200m Bathyal zone: 50m - 4km Abyssal zone: 4km - 6km Hadal zone: 6km + (deepest: Mariana Trench: 11km) Provinces: shallow Continental shelf Wide: passive margins; narrow: active margins Shelf break ~135m, but wide range Continental slope: Submarine canyons Turbidity currents Continental Rise: deep sea fans Provinces: Deep Abyssal plain >4km Ocean ridges, topography on plain Seamounts, guyots: other volcanic activity Trenches >6.7km D Japan Trench 10.5 Mariana Trench 11.0 Philippine Trench 10.8 Aleutian Trench 7.7 Peru-Chile Trench 8.1 Puerto Rico Trench 8.4 Java Trench 7.5 L 2200 2550 1400 3700 5900 1550 4500 W 120 70 55 50 100 120 80 Life in the ocean Horizontal zonation: Geographic range Proximity to resources Latitude (Temperature) Circulation patterns Salinity Vertical zonation (water column) Resources Pressure Temperature Light Water Chemistry Geographic range + vertical zonation Resources, life history, habitat constraints determine
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